This invention relates to a system for establishing and controlling the spatial geometric relationship between a powered towing aircraft and a towed fixed wing glider (unpowered) aircraft during airborne flight conditions.
The airlifting load capabilities of a powered aircraft can be increased if a fixed wing glider aircraft carrying additional load is attached to and towed in flight by the powered aircraft. Airborne towing systems involving a powered towing aircraft connected through a towing cable to an unpowered glider carrying a payload, such as additional personnel, have long been utilized. However, in such systems the glider must carry a pilot who controls the spatial geometric relationship between the towing aircraft and the glider by operating conventional aerodynamic control surfaces of the glider.
A particularly useful aspect of increasing the airlifting load capabilities of both fixed wing and rotary wing powered aircraft would be to have the powered aircraft tow a glider carrying additional fuel which could extend the endurance and range of the towing ("drinking") aircraft or to utilize the towed glider as a tanker from which other aircraft could be refueled in the air. Studies indicate that a towed glider loaded with fuel could quadruple the time on station of a Navy P-3C Orion aircraft due to the additional fuel carried by the towing glider doubling the fuel available to the P-3C Orion aircraft. A fuel loaded glider towed by a rotary wing aircraft would have increased utility over that towed by a fixed wing aircraft since a helicopter has aerodynamic relatively short range characteristics because of its low lift to drag ratio in contrast to the much greater lift to drag ratio of a fixed wing glider being towed by the low lift-drag ratio helicopter.
The optimum position of a towed glider during normal flight is above and behind the towing aircraft to be clear of the downwash of the towing aircraft. The glider must be raised to this position from its takeoff position below that of the towing aircraft. Maintenance of a safe as well as an optimum spatial geometric relationship between the towing aircraft and the load carrying towed glider is essential during airborne flight. The spatial relationship between the towing and towed aircraft is particularly crucial when the glider is being towed by a rotary wing aircraft to ensure that the towing connection is maintained free of the rotational path of the towing helicopter rotor blades. Utilizing a pilot in the glider to maintain the required spatial relationship between the towing and towed aircraft involves a weight penalty and has a further disadvantage that the pilot's visual reference may not be sufficient in night or low visibility operations to maintain the glider at a safe elevated position with respect to a towing rotary wing aircraft. Further, in a number of types of operations, such as utilizing the towed glider to carry additional fuel, operational conditions might require the glider be cut loose or destroyed in flight which precludes utilizing a pilot for the glider. The problem to which this invention is directed is that of establishing a towing arrangement and a remote aerodynamic control system for the glider which will maintain the glider at a safe and optimum spatial geometric relationship to the towing aircraft and at an optimum angle of attack while in airborne flight.